New South Wales Waratahs defence guru Nathan Grey is tipping the Brumbies will display both the daring and grinding aspects of their game in Saturday's all-Australian Super Rugby semi-final.

The Brumbies have shown they can win games this year through both a kick-dominated territory game and expansive running rugby.

Waratahs assistant coach Grey, the man who has helped put the starch and structure into the competition's leading defence this year, expects the Brumbies to switch between styles in their clash at the Sydney Football Stadium.

"I think you're going to see a mix," Grey said.

"They are finding that balance well, when to kick and when to run.

"Certainly it's reflected in their play and also their coaching."

The return from injury of Wallabies five-eighth Matt Toomua has added spark to the Brumbies in their past two games, in which they scored 11 tries, nine of them through backs.

I think you're going to see a mix. (The Brumbies) are finding that balance well, when to kick and when to run.

Waratahs defence coach Nathan Grey

Grey nominated Toomua's running to the line as one of the big attacking threats.

"You can see from the tries that they've scored in the last couple of weeks, but there's lots of threats across the park," Grey said.

"Henry Speight is playing good football and he's a good ball carrier.

"Christian Lealiifano, he's got good feet at the line and he's a strong ball carrier as well.

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